Theoretically,copper–niobium(Cu-Nb)composite superconducting cavities have excellent potential for high thermal and mechanical stability.They can appropriately exploit the high-gradient surface processing recipes dev...Theoretically,copper–niobium(Cu-Nb)composite superconducting cavities have excellent potential for high thermal and mechanical stability.They can appropriately exploit the high-gradient surface processing recipes developed for the bulk niobium(Nb)cavity and the thick copper(Cu)layer’s high thermal conductivity and rigidity,thereby enhancing the operational stability of the bulk Nb cavities.This study conducted a global review of the technical approaches employed for fabricating Cu-Nb composite superconducting cavities.We explored Cu-Nb composite superconducting cavities based on two technologies at the Institute of Modern Physics,Chinese Academy of Sciences(IMP,CAS),including their manufacturing processes,radio-frequency(RF)characteristics,and mechanical performance.These cavities exhibit robust mechanical stability.First,the investigation of several 1.3 GHz single-cell elliptical cavities using the Cu-Nb composite sheets indicated that the wavy structure at the Cu-Nb interface influenced the reliable welding of the Cu-Nb composite parts.We observed the generation and trapping of magnetic flux density during the T_c crossing of Nb in cooldown process.The cooling rates during the T_c crossing of Nb exerted a substantial impact on the performance of the cavities.Furthermore,we measured and analyzed the surface resistance R_(s)attributed to the trapped magnetic flux induced by the Seebeck effect after quenching events.Second,for the first time,a low-beta bulk Nb cavity was plated with Cu on its outer surface using electroplating technology.We achieved a high peak electric field E_(pk)of~88.8 MV/m at 2 K and the unloaded quality factor Q_(0)at the E_(pk)of 88.8 MV/m exceeded 1×10^(10).This demonstrated that the electroplating Cu on the bulk Nb cavity is a practical method of developing the Cu-Nb composite superconducting cavity with superior thermal stability.The results presented here provide valuable insights for applying Cu-Nb composite superconducting cavities in superconducting accelerators with stringent operational stability requirements.展开更多
The electron-doped cuprate superconductor exhibits a unique electronic structure,where both electron and hole Fermi surface(FS)pockets coexist in the optimally doped(OP)region,while in the overdoped(OD)region there ex...The electron-doped cuprate superconductor exhibits a unique electronic structure,where both electron and hole Fermi surface(FS)pockets coexist in the optimally doped(OP)region,while in the overdoped(OD)region there exists only a large hole FS pocket.It is therefore an intriguing question whether or not a p-n junction arises if the OD electron-doped cuprate interfaces with the OP compound.Here,we construct such an in-plane junction by selectively modulating the doping levels in thin films of La_(2-x)Ce_(x)CuO_(4)(LCCO)—a typical electron-doped cuprate.We find that the junction exhibits non-linear,asymmetricⅠ-Ⅴcharacteristics,which are consistent with those of a p-n semiconductor junction,across a wide temperature range from 250 K to 10 K,regardless of the Hall coefficient sign change or the superconducting transition.We attribute these features to a potential barrier formed at the junction,which is set by the band bending in both OD and OP LCCO.展开更多
We used a highly sensitive AC magnetic susceptibility technique to probe superconductivity in elemental titanium(Ti)under extreme pressures to 120 GPa in a diamond anvil cell(DAC).The measurements reveal that the crit...We used a highly sensitive AC magnetic susceptibility technique to probe superconductivity in elemental titanium(Ti)under extreme pressures to 120 GPa in a diamond anvil cell(DAC).The measurements reveal that the critical temperature(Tc)of Ti rises monotonically with increasing pressure,reaching 6.1 K at 120 GPa.Our results confirm the bulk nature of the superconductivity in Ti,as evidenced by a robust diamagnetic response in the AC magnetic susceptibility.Our work provides a routine technique to probe Meissner effect of elemental superconductors at megabar pressures.展开更多
This paper describes the synthesis and characterization of Nb_(2)TiW and Nb_(2)TiMo medium-entropy alloys(MEAs).The Nb_(2)TiW and Nb_(2)TiMo MEAs were successfully synthesized using the arc-melting method.Their struct...This paper describes the synthesis and characterization of Nb_(2)TiW and Nb_(2)TiMo medium-entropy alloys(MEAs).The Nb_(2)TiW and Nb_(2)TiMo MEAs were successfully synthesized using the arc-melting method.Their structures and superconducting properties were investigated through detailed characterization using X-ray diffraction(XRD),resistivity,magnetization,and specific heat measurements.The XRD results confirmed that the obtained Nb_(2)TiW and Nb_(2)TiMo compounds have the same body-centered cubic(BCC)structure and crystallize in the Imˉ3m space group(number 229).Experimental results showed that the superconducting transition temperatures(Tcs)of Nb_(2)TiW and Nb_(2)TiMo are approximately 4.86 and 3.22 K,respectively.The upper and lower critical fields of Nb_(2)TiW are 3.52(2)T and 53.36(2)Oe,respectively,and those of Nb_(2)TiMo are 2.11(2)T and 68.23(3)Oe,respectively.First-principles calculations revealed that the d electrons of Nb,Ti,andMo orW are the dominant contributors to the density of states near the Fermi level.Specific heat measurement results indicated that Nb_(2)TiW and Nb_(2)TMo exhibit BCS full-gap s-wave superconductivity.展开更多
基金supported by the Large Research Infrastructures China initiative Accelerator Driven System(No.2017-000052-75-01-000590)the Youth Innovation Promotion Association of Chinese Academy of Sciences(No.2022422)+1 种基金the Young Scientists of National Natural Science Foundation of China(No.12005275)the Advanced Energy Science and Technology Guangdong Laboratory(No.HND22PTZZYY)。
文摘Theoretically,copper–niobium(Cu-Nb)composite superconducting cavities have excellent potential for high thermal and mechanical stability.They can appropriately exploit the high-gradient surface processing recipes developed for the bulk niobium(Nb)cavity and the thick copper(Cu)layer’s high thermal conductivity and rigidity,thereby enhancing the operational stability of the bulk Nb cavities.This study conducted a global review of the technical approaches employed for fabricating Cu-Nb composite superconducting cavities.We explored Cu-Nb composite superconducting cavities based on two technologies at the Institute of Modern Physics,Chinese Academy of Sciences(IMP,CAS),including their manufacturing processes,radio-frequency(RF)characteristics,and mechanical performance.These cavities exhibit robust mechanical stability.First,the investigation of several 1.3 GHz single-cell elliptical cavities using the Cu-Nb composite sheets indicated that the wavy structure at the Cu-Nb interface influenced the reliable welding of the Cu-Nb composite parts.We observed the generation and trapping of magnetic flux density during the T_c crossing of Nb in cooldown process.The cooling rates during the T_c crossing of Nb exerted a substantial impact on the performance of the cavities.Furthermore,we measured and analyzed the surface resistance R_(s)attributed to the trapped magnetic flux induced by the Seebeck effect after quenching events.Second,for the first time,a low-beta bulk Nb cavity was plated with Cu on its outer surface using electroplating technology.We achieved a high peak electric field E_(pk)of~88.8 MV/m at 2 K and the unloaded quality factor Q_(0)at the E_(pk)of 88.8 MV/m exceeded 1×10^(10).This demonstrated that the electroplating Cu on the bulk Nb cavity is a practical method of developing the Cu-Nb composite superconducting cavity with superior thermal stability.The results presented here provide valuable insights for applying Cu-Nb composite superconducting cavities in superconducting accelerators with stringent operational stability requirements.
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFA1403100)the National Natural Science Foundation of China(Grant Nos.52388201,12361141820,and 12274249)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302400)。
文摘The electron-doped cuprate superconductor exhibits a unique electronic structure,where both electron and hole Fermi surface(FS)pockets coexist in the optimally doped(OP)region,while in the overdoped(OD)region there exists only a large hole FS pocket.It is therefore an intriguing question whether or not a p-n junction arises if the OD electron-doped cuprate interfaces with the OP compound.Here,we construct such an in-plane junction by selectively modulating the doping levels in thin films of La_(2-x)Ce_(x)CuO_(4)(LCCO)—a typical electron-doped cuprate.We find that the junction exhibits non-linear,asymmetricⅠ-Ⅴcharacteristics,which are consistent with those of a p-n semiconductor junction,across a wide temperature range from 250 K to 10 K,regardless of the Hall coefficient sign change or the superconducting transition.We attribute these features to a potential barrier formed at the junction,which is set by the band bending in both OD and OP LCCO.
基金Project supported by the National Key Research and Development Program of China(Grant No.2023YFA1406000)the National Natural Science Foundation of China(Grant No.12204514).
文摘We used a highly sensitive AC magnetic susceptibility technique to probe superconductivity in elemental titanium(Ti)under extreme pressures to 120 GPa in a diamond anvil cell(DAC).The measurements reveal that the critical temperature(Tc)of Ti rises monotonically with increasing pressure,reaching 6.1 K at 120 GPa.Our results confirm the bulk nature of the superconductivity in Ti,as evidenced by a robust diamagnetic response in the AC magnetic susceptibility.Our work provides a routine technique to probe Meissner effect of elemental superconductors at megabar pressures.
基金supported by the National Natural Science Foundation of China(Grant Nos.12274471,12404165,11922415,and 92165204)Guangzhou Science and Technology Programme(Grant Nos.2024A04J6415)+5 种基金the State Key Laboratory of Optoelectronic Materials and Technologies(Sun Yat-Sen University,No.OEMT-2024-ZRC-02)the Key Laboratory of Magnetoelectric Physics and Devices of Guangdong Province(Grant No.2022B1212010008)the Research Center for Magnetoelectric Physics of Guangdong Province(Grant No.2024B0303390001)Guangdong Provincial Quantum Science Strategic Initiative(Grant No.GDZX2401010)Lingyong Zeng acknowledges the Postdoctoral Fellowship Program of CPSF(Grant No.GZC20233299)the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(Grant No.24qupy092)。
文摘This paper describes the synthesis and characterization of Nb_(2)TiW and Nb_(2)TiMo medium-entropy alloys(MEAs).The Nb_(2)TiW and Nb_(2)TiMo MEAs were successfully synthesized using the arc-melting method.Their structures and superconducting properties were investigated through detailed characterization using X-ray diffraction(XRD),resistivity,magnetization,and specific heat measurements.The XRD results confirmed that the obtained Nb_(2)TiW and Nb_(2)TiMo compounds have the same body-centered cubic(BCC)structure and crystallize in the Imˉ3m space group(number 229).Experimental results showed that the superconducting transition temperatures(Tcs)of Nb_(2)TiW and Nb_(2)TiMo are approximately 4.86 and 3.22 K,respectively.The upper and lower critical fields of Nb_(2)TiW are 3.52(2)T and 53.36(2)Oe,respectively,and those of Nb_(2)TiMo are 2.11(2)T and 68.23(3)Oe,respectively.First-principles calculations revealed that the d electrons of Nb,Ti,andMo orW are the dominant contributors to the density of states near the Fermi level.Specific heat measurement results indicated that Nb_(2)TiW and Nb_(2)TMo exhibit BCS full-gap s-wave superconductivity.
